Multi Dimensional Arrays

[Jim Croce]

Hi,
Could someone explain a little to me about multi-dimensional arrays? For example, what does this code say exactly.
int ia [][] = { {1,2}, null };
Thx

[Anonymous]

Actually, according to the Java specification, Java has no "multidimensional" arrays. The Java language only has "arrays of arrays".
Declaring such an array can be done like the following:
int ia[][] = { {1,2,3}, {4,5,6} };
The above declaration creates ia[2][3].

[Bartholemu Smith]

You can think of a 2 demensional array as a Array which has another array inside it.
So:

int ia [][] = { {1,2}, null };

This means basically you have a 2 dimensional array called "ia"
you are predefining the values which will be heald in the array.
Remember a array within a array. {1,2} is index 0 of the bigger array and on the inside 1 is index 0, while 2 is index 1. I hope this is making sense...
the null basically is index 1 of the bigger array, and being null there is not anything there.
anyway..Im sure I probably confused you more than anything...Sorry If i did..hope i helped a little :P
Cheers
Faisal

[Jim Croce]

Thx, I think it is making a little more sense. So in the example that Eric used.
The bigger array will contain 2 elements [0][1],
the [0] element will contain an array with [0][1][2] that will have values of 1,2,3 and the [1] will contain an array of [0][1][2] with the values of 4,5,6.
Is this correct or am I totally off.
Thx

[Thomas Paul]

for int ia [][] = { {1,2}, null };
you will get:
ia[0][0] = 1
ia[0][1] = 2

[Jim Croce]

Thomas,
Would there be an element in [1][0] and [1][1] that will contain null?

[Manfred Leonhardt]

Hi Jim,
From your last reply, it seems you still are confused. Erik is correct in that Java has no multidimensional arrays. What that means is that arrays in java don't have to be square (i.e., same number of columns in every row). Think of multidimensional arrays in java as vectors of vectors. You example will give you the following memory situation:
ia[0][0] --> 1
ia[0][1] --> 2
ia[1] --> null
In other words, we get a triangular array. First row contains 2 columns while the second contains no columns. To see what I am talking about play with the code below.

public class A
{
  public static void main( String[] arg )
  {
    //
    // Define first example
    //  Notice number of columns shrinking in each row.
    //
    int ia[][] = { {1,2,3}, {4,5}, {6} };
    System.out.println( "First example (missing columns!): " );
    for( int i = 0; i < ia.length; ++i )
    {
      for( int j = 0; j < ia[i].length; ++j )
      {
        System.out.print( ia[i][j] + " " );
      }
      System.out.println();
    }
    //
    // Define second example
    //  Notice null pointer when trying to access second row!
    //
    int ia2[][] = { {1,2}, null };
    System.out.println( "Second example (NullPointerException): " );
    for( int i = 0; i < ia2.length; ++i )
    {
      for( int j = 0; j < ia2[i].length; ++j )
      {
        System.out.print( ia2[i][j] + " " );
      }
      System.out.println();
    }
  }
}

Enjoy,
Manfred.

[Jim Croce]

Thx for your help. That makes sense. My next question was actually if the arrays have to have the same number of elements.
Thx